Metal oxide temperature monitor

ABSTRACT

A method, and associated structure, for monitoring temperature and temperature distributions in a heating chamber for a temperature range of 200 to 600° C., wherein the heating chamber may be used in the fabrication of a semiconductor device. A copper layer is deposited over a surface of a semiconductor wafer. Next, the wafer is heated in an ambient oxygen atmosphere to a temperature in the range of 200-600° C. The heating of the wafer oxidizes a portion of the copper layer, which generates an oxide layer. After being heated, the wafer is removed and a sheet resistance is measured at points on the wafer surface. Since the local sheet resistance is a function of the local thickness of the oxide layer, a spatial distribution of sheet resistance over the wafer surface reflects a distribution of wafer temperature across the wafer surface during the heating of the wafer. The measured spatial distribution of sheet resistance may be utilized to readjust the spatial distribution of heat input to another wafer in order to achieve a more uniform temperature across the other wafer&#39;s surface. In addition, the monitor may be reconditioned for repeated use by heating the monitor in a hydrogen ambient environment to convert the oxide layer to unoxidized copper. Additionally, the oxide layer has a color that is a function of the oxide layer thickness, where the color may be used to estimate the temperature at which the wafer was heated in the ambient oxygen atmosphere.

BACKGROUND OF THE INVENTION

[0001] 1. Technical Field

[0002] The present invention relates to a method, and associatedstructure, for monitoring temperature and temperature distributions in aheating chamber for a temperature range of 200 to 600° C., wherein theheating chamber may be used in the fabrication of a semiconductordevice.

[0003] 2. Related Art

[0004] Annealing (i.e., heating) a semiconductor wafer at a uniformtemperature in a range of 200 to 600° C. may be required in a processthat fabricates a semiconductor device. In order to ensure that aheating chamber used for the annealing is at the desired uniformtemperature, particularly at a local space within the heating chamber atwhich the semiconductor wafer is positioned, it is necessary to monitorthe temperature distribution within the local space of the heatingchamber.

[0005] There are currently two methods of externally monitoring andcalibrating temperature control tools used in the annealing. The firsttechnique employs a monitor having a known thermocouple standard.However, this monitor is difficult to use, time consuming and expensive.Furthermore, this monitor indicates the temperature at only a fewisolated locations on the wafer. The second temperature monitoringtechnique uses a second wafer to indicate the temperature across theentire surface of the wafer being fabricated. Currently, there arethermal oxide wafers that are sensitive in a range of about 800° C. toabout 1200° C. There are also activation monitors implanted with n-typeor p-type dopants which are sensitive in a range of about 850° C. toabout 1100° C. Similarly, titanium monitors, which are sputtered withtitanium (Ti) and annealed to form TiSi, have a sensitivity in a rangeof about 650° C. to about 750° C. Likewise, cobalt (Co) monitors exhibita sensitivity in a range of about 530° C. to about 575° C.

[0006] Unfortunately, there are no existing temperature monitors havinga temperature sensitivity within the range of about 200° C. to about600° C. In addition, many of the techniques currently used to monitorannealing temperatures are expensive, time consuming, and difficult touse. Furthermore, none of the above mentioned techniques, with theexception of the thermal oxide monitor, can be reused repeatedly.

[0007] Accordingly, there exists a need for a temperature monitoringdevice for temperatures in the range of about 200° C. to about 600° C.,as well as a need for reconditioning such monitors for repeated usage.

SUMMARY OF THE INVENTION

[0008] The present invention provides a temperature monitoring wafer,comprising:

[0009] a substrate;

[0010] a conductive layer coupled to the substrate, wherein theconductive layer includes a conductive material that will oxidize toform a layer of oxide when the conductive material is at a temperaturein a temperature range of about 200° C. to about and in an oxidizingenvironment that comprises an oxidizer of sufficient concentration tooxidize a portion of the conductive layer such that the layer of oxideis formed, and wherein said layer of oxide is utilizable for saidtemperature monitoring.

[0011] The present invention provides a method of fabricating atemperature monitoring wafer, comprising the steps of:

[0012] providing a substrate; and

[0013] forming a conductive layer on the substrate, wherein theconductive layer includes a conductive material that will oxidize toform an oxide layer when the conductive material is at a temperature ina temperature range of about 200° C. to about 600° C. and in anoxidizing environment that comprises an oxidizer of sufficientconcentration to oxidize a portion of the conductive layer such that theoxide layer is formed, and wherein said oxide layer is utilizable forsaid temperature monitoring.

[0014] The present invention provides a method of fabricating atemperature monitoring wafer, comprising the steps of:

[0015] providing a substrate;

[0016] forming a diffusion barrier layer on the substrate, wherein thediffusion barrier layer inhibits diffusion of a conductive material intothe substrate from a conductive layer when the wafer is at a firsttemperature in a temperature range of about 200° C. to about 600° C.,and wherein the substrate inhibits diffusion of material from thesubstrate into the conductive layer when the wafer is at a secondtemperature in the temperature range, and wherein the first temperatureand the second temperature are equal or unequal; and

[0017] forming the conductive layer on the diffusion barrier layer,wherein the conductive layer includes a conductive material that willoxidize to form an oxide layer when the conductive material is at atemperature in the temperature range and in an oxidizing environmentthat comprises an oxidizer of sufficient concentration to oxidize aportion of the conductive layer such that the oxide layer is formed,said oxide layer utilizable for said temperature monitoring.

[0018] The present invention provides a temperature monitoring device toaccurately monitor a temperature distribution in a heating chamber in a200° C. to 600° C. temperature range. The present invention alsoprovides a method for reconditioning the temperature monitor forrepeated usage. Additionally, the temperature monitor is reliable, easyto use, and inexpensive to fabricate.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 depicts a front cross-sectional view of a semiconductorwafer having a diffusion barrier on a substrate, in accordance with anembodiment of the present invention.

[0020]FIG. 2 depicts the wafer FIG. 1 after a conductive layer has beenformed on the diffusion barrier.

[0021]FIG. 3 depicts the wafer of FIG. 2 under temperature elevation ina heating chamber.

[0022]FIG. 4 depicts the wafer FIG. 3 after a top portion of theconductive layer has been transformed into an oxide layer having anonuniform thickness.

[0023]FIG. 5 depicts the wafer FIG. 3 after a top portion of theconductive layer has been transformed into an oxide layer having auniform thickness.

[0024]FIG. 6 depicts the wafer of FIG. 4 with a sheet resistance beingmeasured at a point on a wafer surface.

[0025]FIG. 7 depicts a plot of sheet resistance of the wafer of FIG. 4(or FIG. 5) versus chamber temperature.

DETAILED DESCRIPTION OF THE INVENTION

[0026]FIG. 1 illustrates a cross-sectional view of a semiconductor wafer10 having a substrate 12, in accordance with an embodiment of thepresent invention. The wafer 10 is a “test wafer” which, after severalprocess steps, will serve as a temperature monitor for determiningtemperature inhomogeneities in a heating chamber, as will be describedinfra. In the context of the present invention, a temperature monitor isa device that is capable of monitoring temperature and temperaturedistributions (i.e., spatial variations in temperature) within a localspace inside a heating chamber. The substrate 12 includes anon-conductive material and may have a same composition that a“production wafer” would have, wherein a production wafer is a waferthat is processed in the heating chamber in conjunction with a realapplication such as a fabrication of a semiconductor device.Accordingly, the substrate 12 may include a semiconductor material thatis doped with n-type material (e.g., arsenic, phosphorus, bismuth,lead), doped with p-type material (e.g., boron, indium, gallium), or notdoped. The semiconductor material may include silicon, but mayalternatively include other semiconductor substances such as galliumarsenide or germanium. Note that an effectiveness of the wafer 10 as atest monitor is insensitive to the material comprised by the substrate12. Accordingly, the substrate 12 may include any material that issufficiently insulative.

[0027] A diffusion barrier layer 14 may be deposited on a surface 13 ofthe substrate 12, using conventional deposition techniques. Thediffusion barrier layer 14 serves to prevent a diffusion of conductivematerial from a conductive layer (see infra FIG. 2 and accompanyingdiscussion) of the wafer 10 into the substrate 12 when the wafer 10 isat a temperature between about 200° C. and about 600° C. The diffusionbarrier layer 14 also serves to prevent a diffusion of material (e.g.,silicon) from the substrate 12 into said conductive layer when the wafer10 is at a temperature between about 200° C. and about 600° C. Note thatthe aforementioned conductive layer is a conductive layer 16 that willbe formed in a subsequent process step, as discussed infra inconjunction with FIG. 2. Said diffusion may cause variability oftemperature monitoring measurements using the wafer 10, which isundesirable. The diffusion barrier layer 14 may include adiffusion-blocking constituent such as tantalum nitride (Ta₂N) orsilicon nitride (Si₃N₄); however, other materials may also be used thatare capable of preventing the diffusion. The diffusion barrier layer 14generally has a thickness greater than about 20 angstroms (Å), andpreferably between about 100 Å and about 500 Å.

[0028]FIG. 2 illustrates the wafer 10 of FIG. 1 after the conductivelayer 16 has been formed on the diffusion barrier 14, wherein theconductive layer 16 includes the conductive material. The conductivelayer 16 may be formed by any method known to one of ordinary skill,such as by being deposited on the diffusion barrier layer 14 usingconventional deposition techniques such as sputtering. The conductivelayer 16 may include, inter alia, copper. However, the conductive layer16 may comprise other conductive materials, including such metals asaluminum, platinum, tungsten, titanium, and cobalt. The conductive layer16 has a thickness between about 100 Å and about 1500 Å, and preferablyabout 600 Å. If the diffusion barrier layer 14 is absent, then theconductive layer 16 is formed directly on the substrate 12 by any methodknown to one of ordinary skill, such as by being deposited on thesubstrate 12 using conventional deposition techniques such assputtering. Thus, the conductive layer 16 is generally coupled to thesubstrate 12, with or without the diffusion barrier layer 14.

[0029]FIG. 3 illustrates the wafer 10 of FIG. 2 being heated in aheating chamber 50 at a heating temperature between about 200° C. andabout 600° C. in an oxygen ambient atmosphere. Generally, the oxygenconcentration in the oxygen ambient atmosphere should be sufficient tooxidize a portion of the conductive layer 16 such that a layer of oxideis formed. The sufficient concentration of oxygen for forming the layerof oxide depends on the conductive material (or materials) of theconductive layer 16 as well as on other parameters such as the heatingtemperature and time of exposure to the heating temperature. Arepresentative sufficient concentration of oxygen corresponds to anoxygen partial pressure of about 1 Torr. The oxygen gas 60 of the oxygenambient atmosphere may be non-flowing in the form of a volumetricdistribution within the heating chamber 50. Alternatively, the oxygengas 60 of the oxygen ambient atmosphere may be in a flowing form at lowflow, wherein said oxygen flow contacts the wafer 10. Since the flowingoxygen gas 60 originates from a source that is likely to besubstantially cooler than the heating temperature, the oxygen flow rateshould be sufficiently slow as to minimize or substantially eliminateheat transfer from the wafer 10 to the flowing oxygen gas 60. Suchinhibition of heat transfer may by any method known to one of ordinaryskill in the art. One such method is for the oxygen flow to be slowenough that the dominant mode of said heat transfer is by naturalconvection rather than by forced convection. As an additionalalternative, the oxygen gas 60 of the oxygen ambient atmosphere may beprimarily in a non-flowing form with supplementary flowing oxygen (atsufficiently low flow as discussed supra) replenishing oxygen gas 60that is dynamically lost from the heating chamber 50. Anotheralternative, using flowing oxygen, includes preheating the flowingoxygen gas 60 to a temperature sufficiently close to the heatingtemperature that said heat transfer is negligible even if said heattransfer occurs by forced convection.

[0030] The ambient oxygen environment serves to oxidize a portion of theconductive layer 16 for temperature monitoring purposes, as will bediscussed infra. While the embodiments described herein utilize a heatedoxygen atmosphere, the scope of the present invention includes anyoxidizer (e.g., heated oxygen) whose concentration is sufficient tooxidize a portion of the conductive layer 16 such that a layer of oxideis formed. Other oxidizers that may be used include, inter alia, gasessuch as nitrous oxide, nitric oxide, ammonia, and ozone. Alternatively,the layer of oxide may be formed by directing a plasma (e.g., ionicoxygen) onto the conductive layer 16.

[0031] The wafer 10 is a “test wafer” whose purpose is to facilitate adetermination of heat source settings within the heating chamber 50 suchthat a uniform temperature in the heating chamber 50 will be achievedwhen a “production wafer” is subsequently placed within the heatingchamber 50 for any purpose, such as for growing a film, or depositing alayer of material on a surface of the production wafer. In particular,the present invention determines heating settings for the heatingchamber 50 that will generate a uniform temperature distribution acrossthe test wafer 10, and subsequently across a production wafer. Thus, theaforementioned heat settings derived for the test wafers maysubsequently be used in a production environment with production wafers.

[0032] The heating chamber 50 in FIG. 3 includes any volumetricenclosure capable of heating an object placed therein. The heatingchamber 50 may be, inter alia, a rapid thermal processing (RTP) tool, aplasma enhanced chemical vapor deposition (PECVD) anneal tool, a siliconvalley group (SVG) furnace anneal tool, a physical vapor deposition(PVD) degassing tool, etc. The heat within the heating chamber 50 may bedirected toward the wafer 10 in the direction 56 from a heat source 52above the wafer 10. The heat within the heating chamber 50 may also bedirected toward the wafer 10 in the direction 58 from a heat source 54below the wafer 10. Either or both of the heat sources 52 and 54 may beutilized in the heating chamber 50. Either or both of the heat sources52 and 54 may be a continuous heat source or a distributed array ofdiscrete heat sources such as a distributed array of incandescent bulbs.Alternatively, the heating chamber 50 may be a furnace.

[0033] Any method of achieving the aforementioned heating temperature inthe heating chamber 50 is within the scope of the present invention. Forexample, with the heating chamber 50 being an RTP heating chamber, thewafer 10 could be inserted into the heating chamber 50 when the heatingchamber 50 is at ambient room temperature, followed by a rapid rampingup of temperature within the heating chamber 50, such as ramping at arate between about 50° C./sec and about 100° C./sec, until the desiredheating temperature is achieved therein. The heating temperature withinthe heating chamber 50 should be measured at a spatial point in theheating chamber 50 near the wafer 10 and preferably as close as possibleto the wafer 10. Note that the heating temperature may deviate inuniformity across a surface 22 of the wafer 10.

[0034] The heating of the wafer 10 in the heating chamber 50 causes anoxygen-exposed upper portion of the conductive layer 16 to oxidize andform an oxide layer 18 shown in FIG. 4, wherein the oxide layer 18includes an oxide of the conductive material of the conductive layer 16.Accordingly, the heating of the wafer 10 transforms the conductive layer16 into the oxide layer 18 and a remaining conductive layer 17 havingthe conductive material. The rate of oxidation depends upon thetemperature to which the wafer 10 is exposed. Accordingly, FIG. 4 showsthe oxide layer 18 as having a variable thickness as a consequence of aspatially varying temperature across the surface 22 of the wafer 10during the heating of the wafer 10 in the heating chamber 50. In FIG. 4,the oxide layer 18 has a nonuniform thickness as illustrated bythicknesses t₁, t₂, and t₃ at an interior location, at an edge 47, andat an edge 48 of the wafer 10, respectively, wherein t₁, t₂, and t₃ havedifferent magnitudes. As will be explained infra, the present inventionexploits the aforementioned variable thickness of the oxide layer 18 tomake adjustments in the spatial distribution of heat generation withinthe heating chamber 50 (see FIG. 3) to subsequently achieve a uniformheating temperature across the surface 22 of the wafer 10. Thus thewafer 10 serves as a temperature monitor of the present invention. Uponachievement of the uniform heating temperature across the surface 22 ofthe wafer 10, the oxide layer 18 will have a uniform thickness. FIG. 5illustrates a result of transforming the conductive layer 16 of FIG. 3into an oxide layer 28 and a conductive layer 27, wherein a heatingtemperature across the surface 22 of the wafer 10 is about uniform,resulting in the oxide layer 28 having about a uniform thickness t.

[0035] After the step of heating the wafer 10 has terminated, the sheetresistance R_(s) at spatial points on the wafer 10 is measured by anytechnique known in the art. As an example, FIG. 6 depicts the wafer 10of FIG. 4 (or FIG. 5) with a sheet resistance R_(s) being measured at apoint 70 on the surface 22 of the wafer 10, using a known four-probetechnique which uses probes 71, 72, 73, and 74, wherein probes 71 and 74are outer probes, and probes 72 and 73 are inner probes. A voltage V₁ isimposed between the outer probes 71 and 74, and a voltage V₂ isindependently imposed between the inner probes 72 and 73. After thesheet resistances R_(s1) and R_(s2) are determined, respectively, basedon measured currents I₁ and I₂ between the outer probes 71 and 74, andthe inner probes 72 and 73, respectively, the sheet resistance at thepoint 70 is calculated as the arithmetic average of R_(s1) and R_(s2).The resistivity of the remaining conductive layer 17 is negligible incomparison with a resistivity of: the oxide layer 18, the diffusionbarrier layer 14, and the substrate 12. The relatively low resistivityof the remaining conductive layer 17 causes the currents (I₁ and I₂) toflow primarily through the remaining conductive layer 17. Also notingthat the substrate 12, the diffusion barrier layer 14, the remainingconductive layer 17, and the oxidize layer 18 are in an electricallyparallel combination, and that the electrical current flows primarilythrough the low-resistance remaining conductive layer 17, the measuredsheet resistance R_(s) of the wafer 10 at the point 70 is a very goodapproximation to the sheet resistance of the remaining conductive layer17 associated with the point 70. Note that the oxidize layer 18 is shownin FIG. 6 as comprising regions 30, 31, and 32. A distinctiondifferentiating the regions 30, 31, and 32 will be discussed infra inconjunction with a use of the wafer 10 as a visual monitoring device.

[0036] The sheet resistance R_(s) of the remaining conductive layer 17at the point 70 is inversely proportional to the thickness of theremaining conductive layer 17, and thus directly proportional to thethickness of the oxide layer 18, at the point 70. Since the thickness ofthe oxide layer 18 varies directly with the rate of oxidation which inturns increases as the heating temperature increases, the sheetresistance R_(s) generally increases as the heating temperatureincreases. Thus the measured spatial variations in sheet resistenceR_(s) across the surface 22 of the wafer 10 reflect correspondingspatial variations in heating temperature across the surface 22 of thewafer 10. Accordingly, the measured distribution of sheet resistanceR_(s) across the surface 22 of the wafer 10 provides guidance as to howthe heat source in the heating chamber 50 should be spatiallyredistributed in order to achieve a greater degree of spatialhomogeneity in the sheet resistence R_(s) across the surface 22 of thewafer 10.

[0037] The preceding sequence of the present invention (heating a testwafer, measuring sheet resistance across the wafer, and adjusting theheat source) may be iteratively repeated several times until asufficiently uniform distribution of sheet resistence R_(s) is measuredusing a plurality of temperature monitoring wafers. Any criterion forevaluating spatial uniformity of sheet resistence R_(s) may be used,such as requiring that a maximum spatial variation, ΔR_(s), in measuredsheet resistance R_(s) over the surface 22 of the wafer 10 should beless than a given value. Another criterion for evaluating spatialuniformity of sheet resistence R_(s) is that a maximum percentagevariation, ΔR_(s)/R_(s), in measured sheet resistance R_(s) over thesurface 22 of the wafer 10 be less than a predetermined percentage.Accordingly, the spatial distribution of the heating by the heat sourceshould be adjusted to make ΔR_(s)/R_(s) less than about thepredetermined percentage. Thus far, ΔR_(s)/R_(s) of less than 1.06% hasbeen achieved within 9 iterations, using wafers having a siliconsubstrate, and having a copper conductive layer 16 (see FIG. 3) thatincludes an initial copper thickness between about 100 Å to about 600 Å.The aforementioned silicon wafers included a diffusion barrier layer 14of either silicon nitride (with a thickness of about 500 Å) or tantalumpentoxide (with a thickness of about 400 Å), wherein the heatingtemperature range included 300° C. to 500° C. The lowest value ofΔR_(s)/R_(s) that may be achieved depends on the number of iterationsutilized and the sensitivity of ΔR_(s) to variations in wafertemperature at a given chamber temperature.

[0038] For a wafer 10 heated for 60 seconds at a temperature in a rangeof 300° C. to 500° C. in an 100% oxygen ambient environment at 760 Torrpartial pressure of oxygen within the heating chamber 50 of FIG. 3, FIG.7 illustrates a spread in R_(s) over the surface 22 of the wafer 10. Thewafer 10 included a copper conductive layer 16 (see FIG. 3) having abouta 600 Å initial thickness, and a Ta₂N diffusion barrier layer 14 ofthickness about 400 Å. The resultant oxide layer 18 (see FIG. 4) had aspatially varying thickness due to heating temperature variations on thesurface 22 of the wafer 10, as discussed supra. The indicated chambertemperature on the abscissa of FIG. 7 is a measured temperature in theheating chamber 50 at a location in close proximity to the wafer 10.Curves 80, 82, and 84 respectively denote the mean, minimum, and maximumvalues of sheet resistance R_(s) at each indicated chamber temperature,with respect to forty-nine (49) spatial points on the surface 22 of thewafer 10 at which the sheet resistance R_(s) was measured. The meancurve 80 represents the arithmetic average over the 49 spatial points.The spatial point associated with the minimum curve 82 at a particularchamber temperature is not necessarily the same spatial point associatedwith the minimum curve 82 at another chamber temperature. The spatialpoint associated with the maximum curve 84 at a particular chambertemperature is not necessarily the same spatial point associated withthe maximum curve 84 at another chamber temperature.

[0039] A set of curves of the type depicted in FIG. 7 may be generatedat the end of each iteration of the method of the present invention,after the sheet resistance R_(s) is measured at all 49 spatial points.The differential between the maximum curve 84 and the minimum curve 82reflects the full range in measured sheet resistance R_(s) variationover 49 spatial points on the surface 22 of the wafer 10 at each chambertemperature. Additionally, the spatial distribution of the sheetresistance R_(s) may be utilized to adjust the temperature distributionwithin the heating chamber 50, particularly where the wafer 10 will beplaced, by spatially redistributing the heat source within the heatingchamber 50 as discussed supra. Adjusting the temperature distribution isfor the purpose of performing the next iteration of the process of thepresent invention, in an effort to narrow the differential between themaximum curve 84 and the minimum curve 82. The preceding steps may berepeated for as many iterations as needed to achieve a desired degree ofspacial uniformity of sheet resistance R_(s). As stated previously, aspatially uniform sheet resistance R_(s) is indicative of a spatiallyuniform wafer temperature. Additionally, a spatially tuned distributionof heating, derived as an adjusted heating distribution of a givenheating chamber 50 by the method of the present invention, may be usedto set an initial heating distribution for heating another wafer inanother heating chamber.

[0040] The process of the present invention is increasingly effective asthe slope of the R_(s) vs. chamber temperature curve of FIG. 7increases, since the highest slope portions of the curve occur whereR_(s) is most sensitive to the heating temperature. In FIG. 7, thehighest slopes occur for chamber temperature between approximately 325°C. and 360° C., and the corresponding sensitivity is approximately 0.5ohms per square/° C. Note that the curves in FIG. 7 are temperatureinsensitive at above 360° C., because at 60 seconds of heating above360° C. under the given test conditions, essentially all of the copperor conductive material within the conductive layer 16 (see FIG. 3) isconverted to the oxide within the oxide layer 18 (see FIG. 4). Thus theheating time period should be less than a heating duration that would berequired to oxidize a total thickness of the conductive layer 16. Thereis also a temperature insensitivity below 330° C. because only a verysmall portion of the conductive material 16 (see FIG. 3) is oxidized,which results in inconsequential variations in the thickness of theremaining conductive layer 17 (see FIG. 4).

[0041] The slope in FIG. 7 could be used to convert a differential inR_(s) at a given chamber temperature T to a variation δT in chambertemperature. Defining δ_(s) as the differential in R_(s) between themaximum curve 84 and the minimum curve 82 at the given temperature T,then δT is calculated as δ_(s)/(dR_(s)/dT), where dR_(s)/dT is the slopeof the mean curve 80 at the temperature T. δ_(s) is calculated bysubtracting R_(s) of the minimum curve 82 from R_(s) of the maximumcurve 84 at the given temperature T. dR_(s)/dT is calculated bynumerical differentiation of the mean curve 80 at the given temperatureT.

[0042] Several factors affect the shape or magnitude of the curves 80,82, and 84 of FIG. 7. A first factor is the time of exposure of thewafer 10 to the chamber temperature. As the time of exposure increases,the curves 80, 82, and 84 shift upward as a consequence of the increasein the oxidation layer 18 thickness and the corresponding decrease inthe remaining conductive layer 17 thickness (see FIG. 4 or FIG. 5). Asecond factor is the material selected for the conductive layer 16,which affects the oxidation rate. For example, the oxidation rate isinherently higher for titanium than for copper. Therefore, titanium maybe better than copper for use at higher temperatures, and vice versa. Athird factor is the thickness of the conductive layer 16. For example,the wafer 10 with a thinner conductive layer 16 (e.g., 100 Å) would bemore sensitive at lower temperatures and/or shorter times (e.g., 200° C.for 30 seconds) than with a thicker conductive layer 16 (approximately1500 Å) at higher temperatures and/or longer times (e.g., 500° C. for120 seconds).

[0043] Although chamber temperatures below 300° C. do not explicitlyappear in FIG. 7, it should be noted that data has been collected as lowas 200° C., and a high as 600° C. with appropriate choices of conductivematerial thicknesses, exposure times, etc. These collected data indicatesufficient sensitivity of sheet resistance R_(s) to temperatures as torender the temperature monitoring associated with the test conditions ofFIG. 7 effective in the chamber temperature range of 200° C. to 600° C.

[0044] If the temperature distribution across a surface 22 of the wafer10 is held constant during the time period of heating the conductivelayer 16, then a resultant sheet resistance R_(s) distribution acrossthe surface 22 of the wafer 10 will be invariant to the time duration ofthe heating, provided that the entire conductive layer 16 has notoxidized. Accordingly, the time duration of heating a production wafermay differ from the time duration of heating the test wafer which wasused to set the heating environment for the production wafer.

[0045] The monitor of the present invention (i.e., the wafer 10 with theoxide layer 18 in FIG. 4) is reliable, easy to use, and inexpensive tofabricate. Additionally, the monitor is reusable, because the monitor iscapable of being reconditioned (i.e., restored to its unoxidized statethat existed before the wafer 10 was heated in the heating chamber 50).Reconditioning a monitor (i.e., the oxidized wafer 10) entailsconverting the oxide layer 18 of the wafer 10 back into the originalconductive material by heating the oxidized wafer 10 at an appropriateconversion temperature as is denoted infra. For example, the wafer 10,with the remaining conductive layer 17 comprising copper and the oxidelayer 18 comprising cuprous oxide (Cu₂O), may be heated in anon-explosive hydrogen ambient environment which may include, interalia, a “forming gas” of: 10% hydrogen and 90% nitrogen, at atmosphericpressure. Alternatively, the hydrogen ambient environment may includeconcentrations of hydrogen higher than 10% (up to 100%) at a reducedtotal pressure as is known by one of ordinary skill in the art to assurethat the hydrogen ambient environment is non-explosive. Thereconditioning may be performed within a heating chamber such asthe-heating chamber 50 of FIG. 5 at the conversion temperature of atleast about 380° C. for at least about 1 second, and preferably at about380° C. for about 1 second. Note that the monitor of the presentinvention could be used to determine and calibrate the conversiontemperature, which overcomes an inability of the related art toaccurately determine the conversion temperature. The preceding processgenerates an exothermic reaction which forms copper and water. The waterflashes or is evaporated from the surface 22 of the wafer 10, leavingthe conductive layer 16 in a pure copper form with no copper oxide.Because the reaction is exothermic, there is (in light of the thinnessof the Cu₂O layer) an abrupt transition from the cuprous oxide (Cu₂O) tocopper (Cu) at a fixed temperature (e.g., about 380° C. or higher),which is independent of the exposure time or thickness of the conductivelayer 16. The chemical reaction of the aforementioned reconditioning is:

Cu₂O+H₂→2Cu+H₂O

[0046] Similar reconditioning may be employed for a conductive layer 16having a conductive material other than copper.

[0047] Reconditioning of the conductive layer 16 may be performed athigher temperatures than 380° C. and/or for a longer time than 1 second,which has been found to increase the resistivity of the conductivematerial. The increased resistivity, which alters the sensitivity andreliability of the monitoring process, is considered due to thediffusion of silicon of the substrate 12 into the conductive layer 16.Therefore, the diffusion barrier 14, which prevents the aforementioneddiffusion of silicon, is particularly important in the event the monitoris repeatedly used, such as more than three times.

[0048] The temperature monitor (i.e., the wafer 10), as describedherein, may also function as a visual monitoring device. In particular,the oxide layer 18 of the wafer 10 can vary in color from a rosy redcolor to a silver green or silver blue color, depending upon thethickness of the oxide layer 18. For example, annealing the wafer 10having a copper conductive layer 16 (about 600 Å thick) of in a 100%oxygen ambient environment for about 60 seconds at 30° C. yields a rosecolor for the oxide layer 18. Annealing the same wafer 10 at 375° C. for60 seconds yields a silver green color for the oxide layer 18. If duringthe annealing, the temperature of the wafer 10 varies spatially on thesurface 22, there may be a corresponding variation in color at differentspatial points associated of the oxide layer 18. For example, sincelarger oxide thicknesses result from higher heating temperatures, theregions 30 and 32 in FIG. 6 may have a silver green color if the heatingtemperature at the regions 30 and 32 was at or near 375° C. for 60seconds, while the regions 30 and 32 in FIG. 6 may have a rose silver ifthe heating temperature at the region 31 was at or near 300° C. for 60seconds. Accordingly, the oxide layer 18 of the wafer 10 has a colorwhose associated wavelength is a function of the thickness of the oxidelayer or, equivalently, of the anneal temperature. Therefore, by fixingthe anneal time, the color changes of the wafer 10 that results from theannealing may be correlated with the anneal temperature, and thus serveas a method for estimating the anneal temperature. The aforementionedcolor change methodology is also an alternative to the sheet resistanceR_(s) measurement method, described supra, for determining temperaturevariations within the heating chamber 50. Note that the sheet resistanceR_(s) measurement method is more sensitive to oxidation thickness and ismore quantitative than is the color change method. Following thereconditioning process, the copper conductive layer 16 returns to theoriginal copper color.

[0049] While particular embodiments of the present invention have beendescribed herein for purposes of illustration, many modifications andchanges will become apparent to those skilled in the art. Accordingly,the appended claims are intended to encompass all such modifications andchanges as fall within the true spirit and scope of this invention.

We claim:
 1. A temperature monitoring wafer, comprising: a substrate; aconductive layer coupled to the substrate, wherein the conductive layerincludes a conductive material that will oxidize to form a layer ofoxide when the conductive material is at a temperature in a temperaturerange of about 200° C. to about 600° C. and in an oxidizing environmentthat comprises an oxidizer of sufficient concentration to oxidize aportion of the conductive layer such that the layer of oxide is formed,and wherein said layer of oxide is utilizable for said temperaturemonitoring.
 2. The wafer of claim 1, wherein the wafer further comprisesa diffusion barrier layer between the substrate and the conductivelayer, wherein the diffusion barrier layer inhibits diffusion of theconductive material into the substrate when the wafer is at a firsttemperature in the temperature range, wherein the diffusion barrierlayer inhibits diffusion of material from the substrate into theconductive layer when the wafer is at a second temperature in thetemperature range, and wherein the first temperature and the secondtemperature are equal or unequal.
 3. The wafer of claim 2, wherein thediffusion barrier layer includes a diffusion-blocking constituentselected from the group consisting of Ta₂N and Si₃N₄.
 4. The wafer ofclaim 2, wherein the diffusion barrier layer has a thickness of at least20 Å.
 5. The wafer of claim 1, wherein the conductive material includesa metal selected from the group consisting of copper, aluminum,platinum, tungsten, titanium, and cobalt.
 6. The wafer of claim 1,further comprising a heating chamber, wherein the wafer is inside theheating chamber, and wherein an annealing temperature inside the heatingchamber is between about 200° C. and about 600°.
 7. The wafer of claim1, further comprising an oxide layer on the conductive layer, said oxidelayer including an oxide of the conductive material, and wherein saidoxide layer is utilizable for said temperature monitoring.
 8. The waferof claim 7, wherein a thickness of the oxide layer is nonuniform.
 9. Thewafer of claim 7, wherein a thickness of the oxide layer is aboutuniform.
 10. The wafer of claim 7, wherein a sheet resistance of thewafer has a maximum variation of about 1.06% over a surface of thewafer.
 11. The wafer of claim 7, wherein a thickness of the oxide layeris a function of a temperature to which the wafer has been previouslyexposed for a fixed period of time, and wherein the temperature to whichthe wafer has been previously exposed for the fixed period of time is inthe temperature range.
 12. The wafer of claim 7, wherein the wafer has acolor whose associated wavelength is a function of a thickness of theoxide layer.
 13. The wafer of claim 1, wherein the wafer has previouslyincluded an oxide layer on the conductive layer, said oxide layerincluding an oxide of the conductive material, wherein the wafer hasbeen previously used for monitoring temperature in the temperaturerange, and wherein the wafer has been reconditioned for further use suchthat the wafer does not include the oxide layer.
 14. The wafer of claim1, wherein the conductive layer has been partially oxidized at thetemperature in the oxygen atmosphere, and further comprising a systemfor monitoring the temperature or monitoring spatial variations in thetemperature along a surface of the wafer.
 15. A method of fabricating atemperature monitoring wafer, comprising the steps of: providing asubstrate; and forming a conductive layer on the substrate, wherein theconductive layer includes a conductive material that will oxidize toform an oxide layer when the conductive material is at a temperature ina temperature range of about 200° C. to about 600° C. and in anoxidizing environment that comprises an oxidizer of sufficientconcentration to oxidize a portion of the conductive layer such that theoxide layer is formed, and wherein said oxide layer is utilizable forsaid temperature monitoring.
 16. The method of claim 15, wherein theconductive material includes a metal selected from the group consistingof copper, aluminum, platinum, tungsten, titanium, and cobalt.
 17. Themethod of claim 15, further comprising heating the wafer for a timeperiod at a wafer temperature within the temperature range and in theoxygen atmosphere having the oxygen concentration, wherein a portion ofthe conductive layer is oxidized to form the oxide layer that includesan oxide of the conductive material, leaving a remaining conductivelayer having the conductive material.
 18. The method of claim 17,wherein the time period is less than a heating duration that would berequired to oxidize a total thickness of the conductive layer.
 19. Themethod of claim 17, wherein a thickness of the oxide layer is aboutuniform over a surface of the wafer.
 20. The method of claim 17, furthercomprising measuring a sheet resistance at a plurality of points on asurface of the wafer, said sheet resistances characterized by a maximumspatial variation ΔR_(s) in measured sheet resistance over the surfaceof the wafer.
 21. The method of claim 20, wherein a spatial distributionof the heating is adjusted to make the maximum percentage variation inthe measured sheet resistance over the surface of the wafer less thanabout 1.06%.
 22. The method of claim 20, wherein a first iteration ofthe method comprises the providing, forming, heating, and measuringsteps, in addition to an adjusting step, wherein the adjusting stepincludes adjusting a spatial distribution of the heating by utilizing aspatial distribution of the measured sheet resistances to reduce ΔR_(s)in a subsequent second iteration that includes repeating the heating andmeasuring steps using a second wafer, and further comprising after themeasuring step: performing the adjusting step; providing the secondwafer comprising a second conductive layer; performing the seconditeration such that ΔR_(s) in the second iteration is less than ΔR_(s)in the first iteration.
 23. The method of claim 22, wherein the step ofproviding a second wafer includes reconditioning the first wafer suchthat the reconditioned first wafer becomes the second wafer.
 24. Themethod of claim 23, wherein the reconditioning step includes heating thefirst wafer in a hydrogen ambient environment such that the oxide withinthe oxide layer is converted to the conductive material.
 25. The methodof claim 24, wherein the conductive material includes copper (Cu),wherein the oxide includes cuprous oxide (Cu₂O), and wherein the heatingin the reconditioning step is at a temperature above about 380° C. forat least about 1 second.
 26. The method of claim 24, wherein thehydrogen ambient environment is at about atmospheric pressure and has acomposition of about 10% hydrogen and about 90% nitrogen.
 27. The methodof claim 22, wherein the heating of the wafer includes heating the waferin a first heating chamber, and further comprising utilizing theadjusted heating distribution of the first heating chamber to set aninitial heating distribution for heating a second wafer in a secondheating chamber.
 28. The wafer of claim 17, wherein the oxide layer hasa color whose associated wavelength is a function of a thickness of theoxide layer.
 29. The method of claim 17, wherein the oxide layer has acolor whose associated wavelength is a function of the temperature. 30.The method of claim 29, further comprising estimating the temperaturebased on the color of the oxide layer.
 31. A method of fabricating atemperature monitoring wafer, comprising the steps of: providing asubstrate; forming a diffusion barrier layer on the substrate, whereinthe diffusion barrier layer inhibits diffusion of a conductive materialinto the substrate from a conductive layer when the wafer is at a firsttemperature in a temperature range of about 200° C. to about 600° C.,and wherein the substrate inhibits diffusion of material from thesubstrate into the conductive layer when the wafer is at a secondtemperature in the temperature range, and wherein the first temperatureand the second temperature are equal or unequal; and forming theconductive layer on the diffusion barrier layer, wherein the conductivelayer includes a conductive material that will oxidize to form an oxidelayer when the conductive material is at a temperature in thetemperature range and in an oxidizing environment that comprises anoxidizer of sufficient concentration to oxidize a portion of theconductive layer such that the oxide layer is formed, said oxide layerutilizable for said temperature monitoring.
 32. The method of claim 31,wherein the diffusion barrier layer includes a diffusion-blockingconstituent selected from the group consisting of Ta₂N and Si₃N₄. 33.The method of claim 31, wherein the diffusion barrier layer has athickness of at least 20 Å.